"It's that increase in the grey seal population that we've seen over the last four decades that's now drawing these sharks closer to shore. The café is open and these sharks have come here to feed," said Greg Skomal, a scientist at the Massachusetts Division of Fisheries.

Constantly advancing technologies allow scientists to determine when sharks will arrive and how long they'll hang around. Harpoon tags on three dozen great whites track their migration to Florida, South Carolina, Georgia, and even Bermuda, and then back north again.

"Over the last four summers we've seen a relative increase in the number of sharks that are coming back," said Skomal.

Last year, a new tagging technique allowed scientists to capture the mammoth sharks on boats, and attach real-time satellite tags.

"So we get a sense of where the shark is each day," said Skomal.

Three whites were tagged on the boat. You can follow their path online on Ocearch.org. Mary Lee is still in Florida. Lydia is slowly heading north.

"I certainly expect white sharks to arrive sometime this month and stay through summer. There probably will be four or five sharks that will stay here through the summer, leaving anywhere from October to December.

Most sightings over the last couple of summers have the great whites staying off Chatham, Monomoy and Orleans. But last summer one shark took up residence further east in Truro, severely inuring a swimmer.

That's put Cape towns on alert. Nine municipalities are splitting state funding to post new signs, and educate the public about safety. Skomal said it's a balancing act, protecting the mighty fish while keeping beach-goers safe.

"I think if we can point out where these sharks are spending the bulk of their time, that's really handy information for all those municipalities that are dealing with this issue. So that's a first step for us: generate the kinds of data that is helpful for the sake of public safety," said Skomal.

There are things swimmers can do to optimize safety from sharks. Don't swim near where seals are spotted and swim in patrolled beaches where there are lifeguards.

Swim in groups and don't go too far from shore. And always take precautions if there are shark-sightings signs.

Images: Where, when Great Whites will return to Cape

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Tourists and summer residents are about to return to Cape beaches, and so are the great white sharks.